Transient response of propionaldehyde formation during CO/H{sub 2}/C{sub 2}H{sub 4} reaction on Rh/SiO{sub 2}
- Univ. of Akron, OH (United States)
The transient response of propionaldehyde formation during ethylene hydroformylation over Rh/SiO{sub 2} has been studied by transient isotopic methods combined with in situ infrared spectroscopy at 0.1-0.5 MPa and 503 K. The transient methods used in this study involved pulsing {sup 13}CO into the CO feed flow and switching from CO to {sup 13}CO flow. The C{sub 2}H{sub 5}{sup 13}CHO response to the {sup 13}CO step input was found to be equivalent to the integration of the C{sub 2}H{sub 5}{sup 13}CHO response to the pulse input with respect to time. The pulse method allows the economical use of costly isotope to obtain the transient information that is commonly acquired from the step method. Analysis of the transient response reveals that the propionaldehyde may be formed via (i) the insertion of CO into adsorbed ethyl species to form the acyl intermediate, (ii) hydrogenation of the acyl intermediate to produce adsorbed propionaldehyde, and (iii) desorption of adsorbed propionaldehyde. Increasing the total reaction pressure (i.e, increasing all partial pressures in the same ratios) increases the rate constant for hydrogenation of the acyl intermediate which has been identified as the rate-determining step for propionaldehyde formation at 0.1 MPa. Increasing the pressure also increases the coverage, but decreases the residence time of intermediates leading to propionaldehyde. Steady-state rate measurements show that increasing reaction pressure decreased the overall activation energy and increased both rate and selectivity for propionaldehyde. The increase in the rate constant for hydrogenation of acyl intermediate can be related to the decrease in the overall activation energy for propionaldehyde formation. Rate constant analysis of the propionaldehyde response shows that the rate constant for propionaldehyde formation exhibits a sharp single distribution. 52 refs., 13 figs., 3 tabs.
- OSTI ID:
- 175711
- Journal Information:
- Journal of Catalysis, Vol. 151, Issue 2; Other Information: PBD: Feb 1995
- Country of Publication:
- United States
- Language:
- English
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